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of bacterial lifestyle is enormous — being a decisive factor in
mediation of bacterial adhesion to a wide range of surfaces, host
cells internalization, multi-cellular aggregation, pathogenesis,
resistance to environmental stresses, and further to the overall
biofilm architecture. It is remarkable that all these qualities are
ascribed to a fold that only recently was considered one of nature's
biggest evolutionary faults.
7.1
Bacterial Biofilms and the Curli
Extracellular Matrix
Biofilm is defined as an organized surface-bound community of
microorganisms sharing the same polymeric matrix.
1
Biofilms
develop on virtually any material that
comes in contact with any
kind of naturally occurring moisture, from blood
to salt water. Up to
now, it has not been possible to devise a
non-toxic coating method
able to prevent biofilm formation. This is problematic when biofilm
colonize biotic surfaces and on an assortment of devices in medical
and food industry.
The transition from a planktonic to community lifestyle in
a biofilm is ultimately made possible by the action of efficient
organelles that act to initially adhere to the surface and later to
maintain attachment between cells in their community. The curli
fibres (also referred as Tafi, thin aggregative fimbriae, in
Salmonella
spp.) are defined as such proteinaceous adhesive surface organelles
expressed by
Enterobacteriaceae
such as
Escherichia
coli
,
Salmonella
spp.,
implicated in
surface colonization and biofilm formation. When visualized under
light or electron microscopy, curli are observed as thin fimbriae,
3-12 nm in width and several micrometers in length. Curli represent
only one component of the extracellular matrix. Other components
are mostly cellulose fibres, but other surface structures may also be
observed, such as type I fimbriae, flagella, and pili, which contribute
to the biofilm development and purpose.
The course of biofilm formation is composed of several steps.
Citrobacter
spp., and
Enterobacter sakazaki
2,3
The first step is reversible surface attachment. Once irreversible
adhesion has been established, micro-colonies are formed and
eventually develop into a matured biofilm, characterized by
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